Hydraulic fracturing composition, method for making and use of same

ABSTRACT

A hydraulic fracturing composition includes: a superabsorbent polymer in an expanded state; a plurality of proppant particles disposed in the superabsorbent polymer; a well treatment agent, and a fluid to expand the superabsorbent polymer into the expanded state. A process for treating a well with well treatment agent includes disposing a hydraulic fracturing composition comprising the well treatment agent in a well. The well treatment agent can be a scale inhibitor, tracer, pH buffering agent, or a combination thereof.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. Nonprovisional patentapplication Ser. No. 14/169,698, filed Jan. 31, 2014, which is acontinuation-in-part of U.S. Nonprovisional patent application Ser. No.13/888,457, filed May 7, 2013, each of which is incorporated byreference in their entirety herein.

BACKGROUND

Hydraulic fracturing increases the flow of desirable fluids such as oiland gas from a subterranean formation and involves placing a fracturingfluid into a subterranean formation or zone at a rate and pressuresufficient to impart a stress in the formation or zone with attendantproduction of a fracture in the formation or zone. Some fracturingfluids contain a viscosifying or gelling agent such as a polysaccharidethat breaks shortly before or after placement in the formation.

Beyond creating the fracture, the fracturing fluid also transports aproppant into the fracture. The proppant is supposed to keep thefracture open after release of the hydraulic pressure. Further, theproppant establishes conductive channels in which the desirable fluidsflow to the borehole. Since the proppant provides a higher conductivitythan the surrounding rock, the fracture has greater potential forproduction of hydrocarbons. However, some fracturing fluids break beforethe fracture closes, and the proppant separates from the fracturingfluid and settles at the bottom of the fracture. In this situation, theproppants settle and concentrate at the bottom of the fracture, and thusthe geometry of the fracture and well productivity is impaired.

Accordingly, compositions and methods that provide relatively highpermeability and that enhance the production of hydrocarbons fromfractured formations are highly desired.

BRIEF DESCRIPTION

The above and other deficiencies are overcome by, in an embodiment, ahydraulic fracturing composition comprising: a superabsorbent polymer inan expanded state and configured to break in response to a breakingcondition; a plurality of proppant particles disposed in thesuperabsorbent polymer prior to release of the plurality of proppantparticles from the superabsorbent polymer in response to breaking thesuperabsorbent polymer; an well treatment agent comprising a scaleinhibitor, a tracer, a buffering agent, or a combination thereof and afluid to expand the superabsorbent polymer into the expanded state.

In an embodiment, a process for disposing a plurality of proppantparticles in a fracture comprises: disposing a hydraulic fracturingcomposition in a downhole environment, the hydraulic fracturingcomposition comprising: a superabsorbent polymer in an expanded stateand configured to break in response to a breaking condition, such that adecomposed polymer is formed from breaking the superabsorbent polymer; aplurality of proppant particles disposed in the superabsorbent polymerprior to release of the plurality of proppant particles from thesuperabsorbent polymer in response to breaking the superabsorbentpolymer; and an well treatment agent comprising a scale inhibitor, atracer, a buffering agent, or a combination thereof; and a fluid toexpand the superabsorbent polymer into the expanded state; forming afracture in the downhole environment; disposing the hydraulic fracturingcomposition in the fracture; breaking the superabsorbent polymer afterforming the fracture; and releasing the plurality of proppant particlesfrom superabsorbent polymer to dispose the plurality of proppantparticles in the fracture.

BRIEF DESCRIPTION OF THE DRAWINGS

The following descriptions should not be considered limiting in any way.With reference to the accompanying drawings, like elements are numberedalike:

FIG. 1 shows proppant particles disposed in a superabsorbent polymer inan expanded state according to an embodiment;

FIG. 2 shows proppant particles disposed in a superabsorbent polymer inan expanded state according to an embodiment;

FIG. 3 shows a superabsorbent polymer in an unexpanded state;

FIG. 4 shows a decomposed polymer and proppant particles;

FIG. 5 shows a hydraulic fracturing composition disposed in a fracturebefore a breaking condition;

FIG. 6 shows a response of the hydraulic fracturing composition of FIG.5 to a breaking condition;

FIG. 7 shows a separated fluid and proppant particles disposed in afracture before the fracture closes;

FIG. 8 shows an effect on fracture size for proppant particles thatsettle before the fracture closes;

FIG. 9 shows proppant particles disposed in guar or a superabsorbentpolymer as a function of time at 180° F.;

FIG. 10 shows addition of a breaker to guar or a superabsorbent polymerat 180° F.;

FIG. 11 shows a fracture cell during injection of a hydraulic fracturingcomposition;

FIG. 12 shows a fracture cell after injection of water into a hydraulicfracturing composition disposed in the fracture cell;

FIG. 13 shows the viscosity difference of a SPP fluid alone and a SPPfluid combined with linear gel systems;

FIG. 14A and FIG. 14B, collectively referred to as FIG. 14, shows theeffect of SPP and a linear gel on the foam quality of a foam fracturingfluid;

FIG. 15 shows a fracture cell after alternating injection of aproppant-containing fluid comprising SPP, proppant particles, a fluid toexpand the SPP, and a proppant-free fluid comprising water and alubricant; and

FIG. 16 shows a fracture cell after alternating injection of aproppant-free fluid comprising SPP fluid and a proppant-containing fluidcomprising water, a lubricant, and proppant particles.

FIG. 17 shows an effect of fluid pH on viscosity for a superabsorbentpolymer.

DETAILED DESCRIPTION

A detailed description of one or more embodiments is presented herein byway of exemplification and not limitation.

It has been found that a hydraulic fracturing composition describedherein creates fractures in a formation and transports proppantparticles into the fractures without changing the geometry of thefractures so that hydrocarbon transmission through the fractures andrecovery are optimized. The proppant particles remain suspended in thehydraulic fracturing composition without settling to the bottom of thefractures, which enhances production from a well.

As shown in FIG. 1, the hydraulic fracturing composition 10 includes asuperabsorbent polymer 12 (e.g., a plurality of superabsorbent polymerparticles 12), a plurality of proppant particles 18 disposed in thesuperabsorbent polymer 12, and a fluid (not shown) to expand thesuperabsorbent polymer 12 into the expanded state. In the expandedstate, the superabsorbent polymer 12 is configured to break in responseto a breaking condition, and a decomposed polymer is formed frombreaking the superabsorbent polymer 12. Upon breaking of thesuperabsorbent polymer 12, the plurality of proppant particles 18 arereleased from the superabsorbent polymer 12.

The superabsorbent polymer 12 includes a plurality of polymer chains 13having internal crosslinks 14 between the polymer chains 13 of thesuperabsorbent polymer 12. In an embodiment, the proppant particles 18are included in a space 22 between adjacent superabsorbent polymerparticles 12. In some embodiments, the proppant particles 18 aredisposed in the space 22 and confined by intra-particle crosslinks 26 ofthe superabsorbent polymer particles 12. It is contemplated that thefluid surrounds an exterior 24 of the superabsorbent polymer 12, itsinterior space 22, inside the particles 12, or a combination thereof.

The superabsorbent polymer 12 is a crosslinked, neutralized or partiallyneutralized polymer that is capable of absorbing large amounts ofaqueous liquids, such as water, brine, acid, or base, with swelling andthe formation of a gel or viscous material, and retains the absorbedfluid under a certain pressure or temperature. The superabsorbentpolymer has internal crosslinks, surface crosslinks, or a combinationthereof. Superabsorbent polymer particles are particles ofsuperabsorbent polymers or superabsorbent polymer compositions. Theacronym SAP may be used in place of superabsorbent polymer,superabsorbent polymer composition, and particles or fibers (and thelike) herein.

The SAP has a hydrophilic network that retains large amounts of aqueousliquid relative to the weight of the SAP. In an embodiment, the SAPsherein are a variety of organic polymers that react with or absorb waterand swell when contacted with an aqueous fluid. Non-limiting examples ofsuch SAPs are a polysaccharide material (that, e.g., in a dry state,absorbs and retains a weight amount of water equal to or greater thanits own weight), poly 2-hydroxyethyl acrylate, polyalkyl acrylate,polyacrylamide, poly methacrylamide, poly vinylpyrrolidone, and polyvinyl acetate. In one embodiment, the SAP is a copolymer of acrylamidewith, for example, maleic anhydride, vinyl acetate, ethylene oxide,ethylene glycol, acrylonitrile, or a combination thereof. Production ofSAPs are, e.g., from acrylamide (AM) or acrylic acid and its salts.

In an embodiment, the SAP is polymerized from nonionic, anionic,cationic monomers, or a combination thereof. Polymerization to form theSAP can be via free-radical polymerization, solution polymerization, gelpolymerization, emulsion polymerization, dispersion polymerization, orsuspension polymerization. Moreover, polymerization can be performed inan aqueous phase, in inverse emulsion, or in inverse suspension.

Examples of nonionic monomers for making the SAP include nonionicmonomers such as acrylamide, methacrylamide, N,N-di(C₁-C₈alkyl)acrylamide such as N,N-dimethylacrylamide, vinyl alcohol, vinylacetate, allyl alcohol, hydroxyethyl methacrylate, acrylonitrile, andderivatives thereof. Such derivatives include, for example, acrylamidederivatives, specifically alkyl-substituted acrylamides oraminoalkyl-substituted derivatives of acrylamide or methacrylamide, andare more specifically acrylamide, methacrylamide, N-methylacrylamide,N-methylmethacrylamide, N,N-dimethylacrylamide, N-ethylacrylamide,N,N-diethylacrylamide, N-cyclohexylacrylamide, N-benzylacrylamide,N,N-dimethylaminopropylacrylamide, N,N-dimethylaminoethylacrylamide,N-tert-butyl acrylamide, N-vinylformamide, N-vinylacetamide,acrylonitrile, methacrylonitrile, or a combination thereof.

Examples of anionic monomers for making the SAP include ethylenicallyunsaturated anionic monomers containing acidic groups including acarboxylic group, a sulfonic group, a phosphonic group, a salt thereof,a derivative thereof, or a combination thereof. In an embodiment, theanionic monomer is acrylic acid, methacrylic acid, ethacrylic acid,maleic acid, maleic anhydride, fumaric acid, itaconic acid,α-chloroacrylic acid, β-cyanoacrylic acid, β-methylacrylic acid(crotonic acid), α-phenylacrylic acid, β-acryloyloxypropionic acid,sorbic acid, α-chlorosorbic acid, 2′-methylisocrotonic acid, cinnamicacid, p-chlorocinnamic acid, β-stearyl acid, citraconic acid, mesaconicacid, glutaconic acid, aconitic acid, 2-acrylamido-2-methylpropanesulphonic acid, allyl sulphonic acid, vinyl sulphonic acid, allylphosphonic acid, vinyl phosphonic acid, or a combination thereof.

Examples of cationic monomers for making the SAP include an N,N-di-C₁-C₈alkylamino-C₁-C₈ alkylacrylate (e.g., N,N-dimethyl amino ethylacrylate), N,N-di-C₁-C₈ alkylamino-C₁-C₈ alkylmethacrylate (e.g.,N,N-dimethyl amino ethyl methacrylate), including a quaternary form(e.g., methyl chloride quaternary forms), diallyldimethyl ammoniumchloride, N,N-di-C₁-C₈ alkylamino-C₁-C₈ alkylacrylamide, and aquaternary form thereof such as acrylamidopropyl trimethyl ammoniumchloride.

In an embodiment, the SAP is an amphoteric SAP, containing both cationicsubstituents and anionic substituents. The cationic substituents andanionic substituents occur in various stoichiometric proportions,including one-to-one, or one substituent is present in a greaterstoichiometric amount than the other substituent. Representativeamphoteric SAPs include terpolymers of nonionic monomers, anionicmonomers and cationic monomers.

In an embodiment, the SAP includes a guar gum and carrageenan. Suitablematerials include those disclosed in Japanese Patent Application No.P2003-154262A, the content of which is incorporated by reference hereinin its entirety.

According to an embodiment, the guar gum used in the SAP includesnatural guar gum as well as enzyme treated guar gum; the latter havingbeen obtained by treating natural guar gum with galactosidase,mannosidase, or another enzyme. The guar gum may further be agalactomannan derivative prepared by treating natural guar gum withchemicals to introduce carboxyl groups, hydroxyl alkyl groups, sulfategroups, phosphate groups, and the like. In addition, in an embodiment, anatural polysaccharide, other than guar and carrageenan, is included.Exemplary natural polysaccharides include starch, cellulose, xanthangum, agar, pectin, alginic acid, tragacanth gum, pluran, gellan gum,tamarind seed gum, cardlan, gum arabic, glucomannan, chitin, chitosan,hyaluronic acid, and the like.

Carrageenan is an ionic linear polysaccharide that includes repeatinggalactose units that individually may be sulfated or unsulfated.Specific carrageenan types include kappa, iota, lambda, and the like. Insome embodiments, a mixture of carrageenan types is used. In a specificembodiment, a carrageenan or a carrageenan-like material that form a gelis used. In addition to natural carrageenan, suitable carrageenansinclude enzyme-treated substances of natural carrageenan or derivatizedcarrageenan, e.g., those prepared by treating natural carrageenan (e.g.,with a chemical) to introduce a functional group (e.g., a carboxylgroup, hydroxyl alkyl group, sulfate group, phosphate group, and thelike).

The SAP includes a plurality of crosslinks among the polymer chains ofthe SAP. According to an embodiment, the crosslinks are covalent andresult from crosslinking the SAP with a crosslinker. In an embodiment,the crosslinker is an ethylenically unsaturated monomer that contains,e.g., two sites of ethylenic unsaturation (i.e., two ethylenicallyunsaturated double bonds), an ethylenically unsaturated double bond anda functional group that is reactive toward a functional group (e.g., anamide group) of the polymer chains of the SAP, or several functionalgroups that are reactive toward functional groups of the polymer chainsof the SAP. In an embodiment, the degree of crosslinking in the SAPherein is selected to control the amount of swelling (i.e., fluidabsorption or volume expansion) of the SAP.

Exemplary crosslinkers include a diacrylamide or methacrylamide of adiamine such as a diacrylamide of piperazine; an acrylate ormethacrylate ester of a di, tri, tetrahydroxy compound includingethyleneglycol diacrylate, polyethyleneglycol diacrylate,trimethylopropane trimethacrylate, ethoxylated trimethylol triacrylate,ethoxylated pentaerythritol tetracrylate, and the like; a divinyl ordiallyl compound separated by an azo group such as a diallylamide of2,2′-azobis(isobutyric acid) or a vinyl or allyl ester of a di or trifunctional acid. Additional crosslinkers include water-solublediacrylates such as poly(ethylene glycol)diacrylate (e.g., PEG 200diacrylate) or PEG 400 diacrylate and polyfunctional vinyl derivativesof a polyalcohol such as ethoxylated (9-20) trimethylol triacrylate.Further examples of the crosslinker include aliphatic unsaturatedamides, such as methylenebisacrylamide or ethylenebisacrylamide;aliphatic esters of polyols or alkoxylated polyols with ethylenicallyunsaturated acids, such as di(meth)acrylates or tri(meth)acrylates ofbutanediol, ethylene glycol, polyglycols, trimethylolpropane; di- andtriacrylate esters of trimethylolpropane (which is oxyalkylated (such asethoxylated) with an alkylene oxide such ethylene oxide); acrylate andmethacrylate esters of glycerol or pentaerythritol; acrylate andmethacrylate esters of glycerol and pentaerythritol oxyethylated with,e.g., ethylene oxide; allyl compounds (such as allyl(meth)acrylate,alkoxylated allyl(meth)acrylate reacted with, e.g., ethylene oxide,triallyl cyanurate, triallyl isocyanurate, maleic acid diallyl ester,poly-allyl esters, tetraallyloxyethane, triallylamine,tetraallylethylenediamine, diols, polyols, hydroxy allyl or acrylatecompounds and allyl esters of phosphoric acid or phosphorous acid); ormonomers that are capable of crosslinking, such as N-methylol compoundsof unsaturated amides, such as of methacrylamide or acrylamide, and theethers derived therefrom. A combination of the crosslinkers also can beemployed.

In an embodiment, the SAP is a particle (or fiber or other format) thatincludes surface crosslinks, which occur external to the interior of theSAP. The surface crosslinks, e.g., result from addition of a surfacecrosslinker to the SAP particle and heat-treatment. The surfacecrosslinks increase the crosslink density of the SAP near its surfacewith respect to the crosslinking density of the interior of the SAP.Some surface crosslinkers have a functional group that is reactivetoward a group of the polymer chains of the SAP, e.g., an acid or amidegroup. The surface crosslinker are one of the previously mentionedcrosslinkers and include a functional group such as an alcohol, amine,aldehyde, or carboxylate group. In an embodiment, surface crosslinkershave multiple different functional groups such as polyols, polyamines,polyaminoalcohols, and alkylene carbonates. Ethylene glycol, diethyleneglycol, triethylene glycol, polyethylene glycol, glycerol, polyglycerol,propylene glycol, diethanolamine, triethanolamine, polypropylene glycol,block copolymers of ethylene oxide and propylene oxide, sorbitan fattyacid esters, ethoxylated sorbitan fatty acid esters, trimethylolpropane,ethoxylated trimethylolpropane, pentaerythritol, ethoxylatedpentaerythritol, polyvinyl alcohol, sorbitol, ethylene carbonate, andpropylene carbonate can be used. The surface crosslinkers also providethe SAP with a chemical property that the polymer chains of the SAP didnot have before surface crosslinking and control chemical properties ofthe SAP, e.g., hydrophobicity, hydrophilicity, or adhesiveness of theSAP to other materials such as minerals (e.g., silicates) or otherchemicals such as petroleum compounds (e.g., hydrocarbons, asphaltene,and the like). Other crosslinkers include borate, titanate, zirconate,aluminate, chromate, or a combination thereof. Boron crosslinkersinclude, e.g., boric acid, sodium tetraborate, encapsulated borates, andthe like. In some embodiments, borate crosslinkers are used withbuffering agents and pH control agents such as sodium hydroxide,magnesium oxide, sodium sesquicarbonate, and sodium carbonate, amines(such as hydroxyalkyl amines, anilines, pyridines, pyrimidines,quinolines, pyrrolidines, and carboxylates such as acetates andoxalates), delay agents such as sorbitol, aldehydes, sodium gluconate,and the like. Zirconium crosslinkers, e.g., zirconium lactates (e.g.,sodium zirconium lactate), triethanolamines, 2,2′-iminodiethanol, or acombination thereof are used in certain embodiments. Titanates forcrosslinking include, e.g., lactates and triethanolamines, and the like.

In an embodiment, the SAP includes a repeat unit that comprises anacrylate, an acrylamide, a vinylpyrrolidone, a vinyl ester (e.g., avinyl acetate), a vinyl alcohol, a derivative thereof, or a combinationthereof. According to an embodiment, the SAP is a polyacrylamide havingcrosslinks that are polyethylene glycol diacrylate. In some embodiments,the SAP is polyacrylic acid, wherein the crosslinks are vinyl esteroligomer. In an embodiment, the SAP is poly(acrylic acid) partial sodiumsalt graft poly(ethylene glycol), which is commercially available fromSigma Aldrich. Further, the SAP can be in a number of formats, includinga particle (e.g., a powder), fiber, strand, braid, and the like, or acombination thereof. The size of the SAP is from 10 μm to 100,000 μm,specifically 50 μm to 10,000 μm, and more specifically 50 μm to 1,000μm. As used herein, “size” refers to the largest linear dimension, e.g.,a diameter in a spherical particle. Particles of the SAP are any shapeincluding spherical, angular, and polyhedral. According to anembodiment, the SAP is a particle with pores or spaces between thepolymer chains of the SAP that admits entrance of a fluid or proppantparticle therein. The hydraulic fracturing composition includes aplurality of SAP particles (or other format such as fiber or braid) thatcoalesces together and form a single mass of SAP, herein also referredto as the superabsorbent polymer (SAP). Moreover, although FIG. 1 showsthe SAP as a plurality of superabsorbent polymer particles 12, the SAPis a plurality of superabsorbent polymer fibers 12 as shown in FIG. 2 insome embodiments. A combination of the various formats of the SAP iscontemplated for some embodiments.

The SAP with crosslinks is useful as a carrier for a fluid or proppantparticles. In a fracturing operation (e.g., hydraulic fracturing), theproppant particles disposed in the SAP remain in the fracture and propopen the fracture when pressure used to form the fracture is released asSAPs are broken in response to the breaking condition. The proppantparticles have a size from 1 μm to 2000 μm, specifically 10 μm to 1000μm, and more specifically 10 μm to 500 μm. Further, the proppantparticles have any shape including spherical, angular, and polyhedraland are monodisperse or polydisperse with an average particle sizedistribution that is unimodal or multimodal, e.g., bimodal.

In an embodiment, due to the relative size of the SAP and the proppantparticles, the proppant particles are disposed between neighboring SAPparticles (FIG. 1 item) 12 or fibers (FIG. 2 item 12), e.g., in pores orchannels formed by voids or spaces 22 between such adjacent SAPparticles or fibers or are disposed within individual SAP particles orfibers in the expanded state of the SAP.

The proppant particles include a ceramic, sand, a mineral, a nutshell,gravel, glass, resinous particles, polymeric particles, or a combinationthereof. In an embodiment, the proppant particles are selected dependingon the particular application of the hydraulic fracturing composition.Examples of the ceramic include an oxide-based ceramic, nitride-basedceramic, carbide-based ceramic, boride-based ceramic, silicide-basedceramic, or a combination thereof. In an embodiment, the oxide-basedceramic is silica (SiO₂), titania (TiO₂), aluminum oxide, boron oxide,potassium oxide, zirconium oxide, magnesium oxide, calcium oxide,lithium oxide, phosphorous oxide, and/or titanium oxide, or acombination thereof. The oxide-based ceramic, nitride-based ceramic,carbide-based ceramic, boride-based ceramic, or silicide-based ceramiccontain a nonmetal (e.g., oxygen, nitrogen, boron, carbon, or silicon,and the like), metal (e.g., aluminum, lead, bismuth, and the like),transition metal (e.g., niobium, tungsten, titanium, zirconium, hafnium,yttrium, and the like), alkali metal (e.g., lithium, potassium, and thelike), alkaline earth metal (e.g., calcium, magnesium, strontium, andthe like), rare earth (e.g., lanthanum, cerium, and the like), orhalogen (e.g., fluorine, chlorine, and the like). Exemplary ceramicsinclude zirconia, stabilized zirconia, mullite, zirconia toughenedalumina, spinel, aluminosilicates (e.g., mullite, cordierite),perovskite, silicon carbide, silicon nitride, titanium carbide, titaniumnitride, aluminum carbide, aluminum nitride, zirconium carbide,zirconium nitride, iron carbide, aluminum oxynitride, silicon aluminumoxynitride, aluminum titanate, tungsten carbide, tungsten nitride,steatite, and the like, or a combination thereof.

Examples of suitable sands for the proppant particles include, but arenot limited to, Arizona sand, Wisconsin sand, Badger sand, Brady sand,and Ottawa sand. In an embodiment, the proppant particles made of amineral such as bauxite are sintered to obtain a hard material. In anembodiment, the bauxite or sintered bauxite has a relatively highpermeability such as the bauxite material disclosed in U.S. Pat. No.4,713,203, the content of which is incorporated by reference herein inits entirety.

Naturally occurring proppant particles include nut shells such aswalnut, coconut, pecan, almond, ivory nut, brazil nut, and the like;seed shells of fruits such as plum, olive, peach, cherry, apricot, andthe like; seed shells of other plants such as maize (e.g., corn cobs orcorn kernels); wood materials such as those derived from oak, hickory,walnut, poplar, mahogany, and the like. Such materials are particlesformed by crushing, grinding, cutting, chipping, and the like.

In an embodiment, the proppant particles are coated, e.g., with a resin.That is, individual proppant particles have a coating applied thereto.In this manner, if the proppant particles are compressed during orsubsequent to, e.g., fracturing, at a pressure great enough to producefine particles therefrom, the fine particles remain consolidated withinthe coating so they are not released into the formation. It iscontemplated that fine particles decrease conduction of hydrocarbons (orother fluid) through fractures or pores in the fractures and are avoidedby coating the proppant particles. Coating for the proppant particlesinclude cured, partially cured, or uncured coatings of, e.g., athermoset or thermoplastic resin. Curing the coating on the proppantparticles occurs before or after disposal of the proppant particles inthe SAP or before or after disposal of the hydraulic fracturingcomposition downhole, for example.

In an embodiment, the coating is an organic compound that includesepoxy, phenolic, polyurethane, polycarbodiimide, polyamide, polyamideimide, furan resins, or a combination thereof. The phenolic resin is,e.g., a phenol formaldehyde resin obtained by the reaction of phenol,bisphenol, or derivatives thereof with formaldehyde. Exemplarythermoplastics include polyethylene, acrylonitrile-butadiene styrene,polystyrene, polyvinyl chloride, fluoroplastics, polysulfide,polypropylene, styrene acrylonitrile, nylon, and phenylene oxide.Exemplary thermosets include epoxy, phenolic (a true thermosetting resinsuch as resole or a thermoplastic resin that is rendered thermosettingby a hardening agent), polyester resin, polyurethanes, epoxy-modifiedphenolic resin, and derivatives thereof.

In an embodiment, the curing agent for the coating isnitrogen-containing compounds such as amines and their derivatives;oxygen-containing compounds such as carboxylic acid terminatedpolyesters, anhydrides, phenol-formaldehyde resins, amino-formaldehyderesins, phenol, bisphenol A and cresol novolacs, phenolic-terminatedepoxy resins; sulfur-containing compounds such as polysulfides,polymercaptans; and catalytic curing agents such as tertiary amines,Lewis acids, Lewis bases; or a combination thereof.

In an embodiment, the proppant particles include a crosslinked coating.The crosslinked coating typically provides crush strength, orresistance, for the proppant particles and prevents agglomeration of theproppant particles even under high pressure and temperature conditions.In some embodiments, the proppant particles have a curable coating,which cure subsurface, e.g. downhole or in a fracture. The curablecoating cures under the high pressure and temperature conditions in thesubsurface reservoir. Thus, the proppant particles having the curablecoating are used for high pressure and temperature conditions.

According to an embodiment, the coating is disposed on the proppantparticles by mixing in a vessel, e.g., a reactor. Individual components,e.g., the proppant particles and resin materials (e.g., reactivemonomers used to form, e.g., an epoxy or polyamide coating) are combinedin the vessel to form a reaction mixture and are agitated to mix thecomponents. Further, the reaction mixture is heated at a temperature orat a pressure commensurate with forming the coating. In anotherembodiment, the coating is disposed on the particle via spraying such asby contacting the proppant particles with a spray of the coatingmaterial. The coated proppant particles are heated to inducecrosslinking of the coating.

In addition to the proppant particles and the SAP, the hydraulicfracturing composition includes a breaker in some embodiments. Thebreaker contacts the SAP to break the SAP. In an embodiment, the breakercontacts the SAP and breaks a bond in the backbone of the polymer chainsof the SAP, a bond in the crosslinker, a bond between the crosslinkerand a polymer chain of the SAP, or a combination thereof. That is,breaking the SAP includes disintegrating, decomposing, or dissociatingthe SAP such as by breaking bonds in the backbone of the SAP, breakingcrosslinks among chains of the SAP, changing a geometrical conformationof the superabsorbent polymer, or a combination thereof. In this way,the viscosity of the hydraulic fracturing composition decreases. In someembodiments, the breaker breaks the SAP to form a decomposed polymersuch as a plurality of fragments that have a lower molecular weight thanthe SAP. After breaking the SAP, the plurality of proppant particles isreleased from the SAP.

According to an embodiment, the breaker includes an oxidizer such as aperoxide, a persulfate, a perphosphate, a perborate, a percarbonate, apersilicate, an oxyacid of a halogen, an oxyanion of halogen, a peracid,a derivative thereof, or a combination thereof.

In one embodiment, the breaker is persulfate, such as sodium persulfate,ammonium persulfate, potassium persulfate, potassium peroxymonosulfate(Caro's acid), or a combination thereof. The breaker is, e.g., anoxyacid or oxyanion of halogen, for instance, hypochlorous acid, ahypochlorite, chlorous acid and chlorites, chloric acid and chlorates,perchloric acid and perchlorate, a derivative thereof, or a combinationthereof.

In an embodiment, a peroxide breaker has oxygen-oxygen single bonds inits molecular structure. The peroxide breaker is hydrogen peroxide oranother material to provide peroxide or hydrogen peroxide for breakingthe SAP. Metal peroxides such as sodium peroxide, calcium peroxide, zincperoxide, magnesium peroxide, or other peroxides such as superoxides,organic peroxides, and the like can be used.

Additionally, in an embodiment, the peroxide breaker is a stabilizedperoxide breaker with the hydrogen peroxide bound, inhibited, or thelike by another compound or molecule prior to contact with, e.g., anaqueous fluid such as water such that it forms or releases hydrogenperoxide when contacted by the aqueous fluid. Exemplary stabilizedperoxide breakers include an adduct of hydrogen peroxide with anothermolecule and include carbamide peroxide or urea peroxide(C(═O)(NH₂)₂.H₂O₂), a percarbonate (e.g., sodium percarbonate(2Na₂CO₃.3H₂O₂), potassium percarbonate, ammonium percarbonate, and thelike), and the like. The stabilized peroxide breakers also includecompounds that undergo hydrolysis in water to release hydrogen peroxide,e.g., sodium perborate. In an embodiment, hydrogen peroxide stabilizedwith appropriate surfactants also is used as the stabilized peroxidebreaker.

According to an embodiment, the breaker is the peracid, e.g., peraceticacid, perbenzoic acid, a derivative thereof, or a combination thereof.Additionally, a variety of peroxycarboxylic acids is employed as theperacid breaker. The peroxycarboxylic acid includes an esterperoxycarboxylic acid, an alkyl ester peroxycarboxylic acid, asulfoperoxycarboxylic acid, or a combination thereof. Peroxycarboxylicacid (or percarboxylic acid) are acids having a general formulaR(CO₃H)_(n). In an embodiment, the R group is saturated or unsaturatedas well as substituted or unsubstituted. As described herein, R is analkyl, alkenyl, arylalkyl, arylalkenyl, cycloalkyl, cycloalkenyl,aromatic, heterocyclic, or ester group, or a combination thereof (e.g.,an alkyl ester group), with n being 1, 2, or 3. Exemplary ester groupsinclude aliphatic ester groups, such as R¹OC(O)R², where R¹ and R²independently are a group (e.g., an alkyl group) described above for Rsuch that R¹ and R² are, e.g., independently small carbon chain alkylgroups, such as a C₁-C₅ alkyl group.

One skilled in the art will appreciate that peroxycarboxylic acids maynot be as stable as carboxylic acids, and their stability may increasewith increasing molecular weight. Thermal decomposition of the peracidsproceeds by, e.g., free radical and nonradical paths, byphotodecomposition or radical-induced decomposition, or by the action ofmetal ions or complexes. In an embodiment, the percarboxylic acidperacids are made by direct, acid catalyzed equilibrium action ofhydrogen peroxide with a carboxylic acid, by autoxidation of aldehydes,or from acid chlorides, and hydrides, or carboxylic anhydrides withhydrogen or sodium peroxide.

Exemplary peroxycarboxylic acids include peroxyformic, peroxyacetic,peroxypropionic, peroxybutanoic, peroxypentanoic, peroxyhexanoic,peroxyheptanoic, peroxyoctanoic, peroxynonanoic, peroxydecanoic,peroxyundecanoic, peroxydodecanoic, peroxylactic, peroxycitric,peroxymaleic, peroxyascorbic, peroxyhydroxyacetic (peroxyglycolic),peroxyoxalic, peroxymalonic, peroxysuccinic, peroxyglutaric,peroxyadipic, peroxypimelic, peroxysuberic, peroxysebacic acid, and thelike.

In an embodiment, the peracid includes a combination of severalperoxycarboxylic acids. According to one embodiment, the compositionincludes a C₂-C₄ peroxycarboxylic acid, a C₈-C₁₂ peroxycarboxylic acid,an ester peroxycarboxylic acid, an alkyl ester peroxycarboxylic acids,or a mono- or di-peroxycarboxylic acid having up to 12 carbon atoms, andmore specifically 2 to 12 carbon atoms. In an embodiment, theperoxycarboxylic acid includes peroxyacetic acid (POAA) (i.e., peraceticacid having the formula CH₃COOOH) or peroxyoctanoic acid (POOA) (i.e.,peroctanoic acid having the formula, e.g., of n-peroxyoctanoic acid:CH₃(CH₂)₆COOOH).

In an embodiment, the peracid is an ester peroxycarboxylic acid. As usedherein, ester peroxycarboxylic acid refers to a molecule having theformula:

wherein R¹ and R² are independently an organic group (e.g., alkyl,linear or cyclic, aromatic or saturated) or a substituted organic group(e.g., with a heteroatom or organic group). In an embodiment, the esterperoxycarboxylic acid is made by employing methods used for makingperoxycarboxylic acid such as combining the corresponding estercarboxylic acid with an oxidizing agent, e.g., hydrogen peroxide.

Exemplary alkyl esterperoxycarboxylic acids include monomethylmonoperoxyglutaric acid, monomethyl monoperoxyadipic acid, monomethylmonoperoxyoxalie acid, monomethyl monoperoxymalonic acid, monomethylmonoperoxysuccinic acid, monomethyl monoperoxypimelic acid, monomethylmonoperoxysuberic acid, and monomethyl monoperoxysebacic acid; monoethyl monoperoxyoxalic acid, monoethyl monoperoxymalonic acid, monoethylmonoperoxysuccinic acid, monoethyl monoperoxyglutaric acid, monoethylmonoperoxyadipic acid, monoethyl monoperoxypimelic acid, monoethylmonoperoxysuberic acid, and monoethyl monoperoxysebacic acid; monopropylmonoperoxyoxalic acid, monopropyl monoperoxymalonic acid, monopropylmonoperoxysuccinic acid, monopropyl monoperoxyglutaric acid, monopropylmonoperoxyadipic acid, monopropyl monoperoxypimelic acid, monopropylmonoperoxysuberic acid, monopropyl monoperoxysebacic acid, in whichpropyl is n- or isopropyl; monobutyl monoperoxyoxalic acid, monobutylmonoperoxymalonic acid, monobutyl monoperoxysuccinic acid, monobutylmonoperoxyglutaric acid, monobutyl monoperoxyadipic acid, monobutylmonoperoxypimelic acid, monobutyl monoperoxysuberic acid, monobutylmonoperoxysebacic acid, in which butyl is n-, iso-, or t-butyl; and thelike.

In some embodiments, the peracid breaker is a sulfoperoxycarboxylicacid. Sulfoperoxycarboxylic acids, which also are referred to assulfonated peracids, include the peroxycarboxylic acid form of asulfonated carboxylic acid. In some embodiments, the sulfonated peracidis a mid-chain sulfonated peracid, i.e., a peracid that includes asulfonate group attached to a carbon that is at least one carbon (e.g.,at least the three position) from the carbon of the percarboxylic acidgroup in the carbon backbone of the percarboxylic acid chain, whereinthe at least one carbon is not in the terminal position. As used herein,the term “terminal position” refers to the carbon on the carbon backbonechain of a percarboxylic acid that is furthest from the percarboxylgroup. Thus, in an embodiment, sulfoperoxycarboxylic acid has thefollowing formula:

wherein R³ is hydrogen or a substituted or unsubstituted alkyl group; R⁴is a substituted or unsubstituted alkyl group; X is hydrogen, a cationicgroup, or an ester forming moiety; or salts or esters thereof.

In some embodiments, R³ is a substituted or unsubstituted C_(m) alkylgroup; X is hydrogen, a cationic group, or an ester forming moiety; R⁴is a substituted or unsubstituted C_(n) alkyl group; m=1 to 10; n=1 to10; and m+n is less than 18; or salts, esters, or a combination thereof.In some embodiments, R³ is hydrogen. In other embodiments, R³ is asubstituted or unsubstituted alkyl group. In some embodiments, R³ is asubstituted or unsubstituted alkyl group that does not include acycloalkyl group. In some embodiments, R³ is a substituted alkyl group.In some embodiments, R³ is an unsubstituted C₁-C₉ alkyl group. In someembodiments, R³ is an unsubstituted C₇ or C₈ alkyl. In otherembodiments, R³ is a substituted C₈-C₁₀ alkyl group. In someembodiments, R³ is a substituted C₈-C₁₀ alkyl group and is substitutedwith at least 1, or at least 2 hydroxyl groups. In still yet otherembodiments, R³ is a substituted C₁-C₉ alkyl group. In some embodiments,R³ ₁ is a substituted C₁-C₉ substituted alkyl group and is substitutedwith an —SO₃H group. In other embodiments, R³ is a C₉-C₁₀ substitutedalkyl group. In some embodiments, R³ is a substituted C₉-C₁₀ alkyl groupwherein at least two of the carbons on the carbon backbone form aheterocyclic group. In some embodiments, the heterocyclic group is anepoxide group.

In an embodiment, R⁴ is a substituted C₁-C₁₀ alkyl group. In someembodiments, R⁴ is a substituted C₈-C₁₀ alkyl. In some embodiments, R⁴is an unsubstituted C₆-C₉ alkyl. In other embodiments, R⁴ is a C₈-C₁₀alkyl group substituted with at least one hydroxyl group. In someembodiments, R⁴ is a C₁₀ alkyl group substituted with at least twohydroxyl groups. In other embodiments, R⁴ is a C₈ alkyl groupsubstituted with at least one —SO₃H group. In some embodiments, R⁴ is asubstituted C₉ group, wherein at least two of the carbons on the carbonbackbone form a heterocyclic group. In some embodiments, theheterocyclic group is an epoxide group. In some, embodiments, R⁴ is aC₈-C₉ substituted or unsubstituted alkyl, and R⁴ is a C₇-C₈ substitutedor unsubstituted alkyl.

According to an embodiment, in the hydraulic fracturing composition, thebreaker is encapsulated in an encapsulating material to prevent thebreaker from contacting the SAP. The encapsulating material isconfigured to release the breaker in response to the breaking condition.The breaker is a solid or liquid. As a solid, the breaker is, e.g., acrystalline or granular material. In an embodiment, the solid isencapsulated or provided with a coating to delay its release or contactwith the SAP. Encapsulating materials are the same or different as thecoating material noted above with regard to the proppant particles.Methods of disposing the encapsulating material on the breaker are thesame or different as for disposing the coating on the proppantparticles. In an embodiment, a liquid breaker is dissolved in an aqueoussolution or another suitable solvent.

In an embodiment, the encapsulation material is a polymer that releasesthe breaker in a controllable way, e.g., at a controlled rate orconcentration. Such material is a polymer that degrades over a period oftime to release the breaker and is chosen depending on the release ratedesired. Degradation of the polymer of the encapsulation materialpolymer occurs, e.g., by hydrolysis, solvolysis, melting, and the like.In an embodiment, the polymer of the encapsulation material is ahomopolymer or copolymer of glycolate and lactate, a polycarbonate, apolyanhydride, a polyorthoester, a polyphosphazene, or a combinationthereof.

According to an embodiment, the encapsulated breaker is an encapsulatedhydrogen peroxide, encapsulated metal peroxides (e.g., sodium peroxide,calcium peroxide, zinc peroxide, and the like) or any of the peracids orother breaker herein.

In the hydraulic fracturing composition, the fluid is included tocontact and expand the SAP into the expanded state. The fluid is anaqueous fluid that includes water, brine, an acid such as a mineral acidor an organic acid, or a base. The brine is, for example, seawater,produced water, completion brine, or a combination thereof. Theproperties of the brine can depend on the identity and components of thebrine. Seawater, as an example, contains numerous constituents such assulfate, bromine, and trace metals, beyond typical halide-containingsalts. In some embodiments, produced water is water extracted from aproduction reservoir (e.g., hydrocarbon reservoir) or produced from theground. Produced water also is referred to as reservoir brine andcontains components such as barium, strontium, and heavy metals. Inaddition to the naturally occurring brines (seawater and producedwater), completion brine is synthesized from fresh water by addition ofvarious salts such as KCl, NaCl, ZnCl₂, MgCl₂, or CaCl₂ to increase thedensity of the brine, such as 10.6 pounds per gallon of CaCl₂ brine.Completion brines typically provide a hydrostatic pressure optimized tocounter the reservoir pressures downhole. In an embodiment, the abovebrines are modified to include an additional salt. In an embodiment, theadditional salt included in the brine is NaCl, KCl, NaBr, MgCl₂, CaCl₂,CaBr₂, ZnBr₂, NH₄Cl, sodium formate, cesium formate, and the like. Thesalt is present in the brine in an amount from about 0.5 weight percent(wt %) to about 50 wt %, specifically about 1 wt % to about 40 wt %, andmore specifically about 1 wt % to about 25 wt %, based on the weight ofthe fluid.

According to an embodiment, the fluid is a mineral acid that includeshydrochloric acid, nitric acid, phosphoric acid, sulfuric acid, boricacid, hydrofluoric acid, hydrobromic acid, perchloric acid, or acombination thereof. In some embodiments, the fluid is an organic acidthat includes a carboxylic acid, sulfonic acid, or a combinationthereof. Exemplary carboxylic acids include formic acid, acetic acid,chloroacetic acid, dichloroacetic acid, trichloroacetic acid,trifluoroacetic acid, propionic acid, butyric acid, oxalic acid, benzoicacid, phthalic acid (including ortho-, meta- and para-isomers), and thelike. Exemplary sulfonic acids include alkyl sulfonic acid or arylsulfonic acid. Alkyl sulfonic acids include, e.g., methane sulfonicacid. Aryl sulfonic acids include, e.g., benzene sulfonic acid ortoluene sulfonic acid. In one embodiment, the alkyl group may bebranched or unbranched and contains from one to about 20 carbon atomsand is substituted or unsubstituted. In an embodiment, the aryl group isalkyl-substituted, i.e., is an alkylaryl group, or is attached to thesulfonic acid moiety via an alkylene group (i.e., an arylalkyl group).In an embodiment, the aryl group is substituted with a heteroatom. Thearyl group has from 3 carbon atoms to 20 carbon atoms and includes,e.g., a polycyclic ring structure.

In an embodiment, the hydraulic fracturing composition further includesa well treatment agent for flow assurance, performance enhancement, andfluid stability. Suitable well treatment agents include those that canaddress undesired effects caused by scale formation, salt formation,paraffin deposition, asphaltene deposition, foaming agent deposition,emulsification, gas hydrate formation, corrosion, foaming agents, oxygenscavengers, H₂S scavengers, biocides, surfactants, or a combinationthereof. Specific well treatment agents include a scale inhibitor, atracer, a pH-buffering agent, or a combination thereof.

The well treatment agents can be used in liquid or solid form, as-is orin the form of a salt or other complex. The well treatment agent can becoated, encapsulated, incorporated into a binder, adsorbed onto amatrix, or absorbed into a matrix. Suitable coatings include thethermoplastic, thermosetting, and crosslinked coatings described abovefor use with proppants. Suitable encapsulants include those describedabove for use with breakers. The same thermoplastic, thermosetting, andcrosslinked materials that can be used as a coating or an encapsulantare also suitable for use as a binder, or a matrix for adsorption of thewell treatment agents. Matrices for absorption of the well treatmentmaterials are porous, preferably microporous, and can be organic (e.g.,an open-celled polymer foam such as a polyurethane foam) or inorganic(e.g., zeolites, metal silicates, and aluminophosphates).

Scale inhibitors can be used to control or prevent scale formation inthe well, among other functions. Scale inhibitors can be a carboxylic,sulfonic, or phosphonic acid-containing compound, a carboxylic,sulfonic, or phosphonic-containing polymer, or a combination thereof,for example amino trimethylene phosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, 2-phosphonobutane-1,2,4-tricarboxylicacid, 2-hydroxyethyl-amino-bis(methylenephosphonic acid),ethylenediamine tetrakis(methylene phosphonic acid),tetramethylenediamine tetrakis(methylene phosphonic acid),hexamethylenediamine tetrakis(methylene phosphonic acid), 2-hydroxyphosphonoacetic acid, diethylene triamine penta(methylene phosphonicacid), bis(hexamethylenetriamine penta(methylene phosphonic acid)),polyaminopolyether methylenephosphonate or a salt thereof,phosphino-polycarboxylate, polyacrylic acid, polymaleic acid, acrylicacid copolymers, sulfonated polyacrylate copolymers, polyvinylsulfonate, carboxymethyl inulin, polyaspartate, or a combinationthereof.

The scale inhibitor is present in the hydraulic fracturing compositionin an amount effective to inhibit scale to the desired degree, which canbe, for example, about 0.001 wt % to about 10 wt %, or about 0.01 wt %to about 10 wt %, or about 0.01 wt % to about 5 wt %, preferably about0.1 wt % to about 2 wt %, each based on total weight of the composition.

A tracer can be used to later detect or infer information about thewell, borehole or the drilled formations. Tracers used during drillingcan be mud tracers and filtrate tracers. Tracers can be oil- orwater-soluble. Examples of tracers include a fluorinated benzoic acid,perfluorinated hydrocarbon, alcohol, ketone, organic acid, halogenatedcompound, or a combination thereof.

Exemplary perfluorinated hydrocarbons are perfluorinated C₁-C₁₈hydrocarbons, for example, tetrafluoromethane, tetrafluoroethane,tetrafluoropropane, and the like.

Examples of alcohols include C₁-C₂₄ monofunctional and polyfunctionalalcohols such as methanol, ethanol, glycol, propanol, propanediol,butanol, pentanol, pentaerythritol, hexanol, octanol, decanol,dodecanol, and the like. Preferred alcohols are C₁₀-C₂₄ monofunctionalalcohols.

Exemplary ketones are C₁-C₁₈ ketones and diketones such as acetone,cyclopropanone, methyl ethyl ketone, cyclohexanone, acetylacetone,benzophenone, and the like.

Exemplary organic acids include C₁-C₁₈ mono-, di and tricarboxylicacids. Examples of organic acids are acetic acid, propanoic acid,butanoic acid, oxalic acid, malonic acid, succinic acid, glutaric acid,adipic acid, sebacic acid, citric acid, and the like.

The halogenated compounds can be mono, di, tri and tetrachlorinatedC₁-C₁₂ hydrocarbons. Examples include methylene chloride, chloroform,carbon tetrachloride, trichloroethylene, tetrachloroethylene,hexachlorocyclohexane, benzyl chloride, benzal chloride,benzotrichloride, and the like.

The tracer is present in the hydraulic fracturing composition in anamount effective to trace the desired fluid or composition, which canbe, for example, about 0.001 wt % to about 10 wt %, or about 0.001 wt %to about 5 wt %, or about 0.01 wt % to about 5 wt %, preferably about0.01 wt % to about 1 wt %, each based on total weight of thecomposition.

A buffering agent can be a weak acid or base used to maintain the pH ofa solution near a chosen value after the addition of another acid orbase. The function of a buffering agent is to prevent a rapid change inpH when acids or bases are added to the solution. For buffers in acidregions, the pH is adjusted to a desired value by adding a strong acidsuch as HCl to the buffering agent. For alkaline buffers, a strong basesuch as NaOH is added. Alternatively, a buffer combination can be madefrom a combination, e.g., a mixture, of an acid and its conjugate base.For example, an acetate buffer can be made from a mixture of acetic acidand sodium acetate. Similarly, an alkaline buffer can be made from amixture of the base and its conjugate acid. pH-Buffering agents differfrom pH-adjusting agents in that a buffering agent maintains the pH ofthe fluid in a desired range, for example a pH from about 6 to about 9,preferably a pH from about 6.5 to about 8.5, most preferably a pH ofabout 7 to about 8 at a downhole temperature of a subterranean well.Examples of buffering agents include alkali and alkaline earth salts ofcarbonates, bicarbonate, acetate, citrate, gluconate, phosphate, borate,or tartrate, for example sodium carbonate and potassium carbonate,CaCO₃, sodium sesquicarbonate, and potassium sesquicarbonate, oxides ofalkaline earth metals such as MgO and CaO, an organic polyelectrolytes,or a combination thereof.

The buffering agent is present in the hydraulic fracturing compositionin an amount effective to buffer the composition, which can be, forexample, about 0.005 wt % to about 10 wt %, or about 0.01 wt % to about10 wt %, or about 0.01 wt % to about 5 wt %, or about 0.1 wt % to about2 wt %, each based on total weight of the composition.

The buffering agent can optionally be used in combination with aslow-release breaking agent, for example, a slow release acid. The acidcan be glyoxal, a solid acid, an encapsulated acid, a coated acid, or acombination thereof. Glyoxal is a dialdehyde that can slowly releaseacids. Slow release of acids can overcome the buffering agent, andresult in gradual reduction of the fluid pH until a selected pH value isattained that is suitable for breaking the SAP.

When used, the foregoing well treatment agents can be continuouslyinjected through a downhole injection point in the completion, orperiodic squeeze treatments can be undertaken to place the additive inthe reservoir matrix for subsequent commingling with produced fluids.

Besides the SAP, the hydraulic fracturing composition includes a viscouspolymer in some embodiments. The viscous polymer includes guar gums,high-molecular weight polysaccharides composed of mannose and galactosesugars, xanthan gum, guar, or starch or guar derivatives such ashydropropyl guar (HPG), carboxymethyl guar (CMG), andcarboxymethylhydroxypropyl guar (CMHPG), galactomannan gums, glucomannangums, guars, derived guars, cellulose derivatives, or a combinationthereof. Cellulose derivatives such as hydroxyethylcellulose (HEC),carboxymethylcellulose (CMC), hydroxypropylcellulose (HPC), andcarboxymethylhydroxyethylcellulose (CMHEC); hydropropyl starch; orlignosulfonate also is used.

According to an embodiment, the viscous polymer is includes a repeatunit that comprises an acrylate, an acrylamide, a vinylpyrrolidone, avinyl ester (e.g., a vinyl acetate), a vinyl alcohol, a2-acrylamide-2-methylpropanesulfonic acid, a derivative thereof, or acombination thereof. In some embodiments, the viscous polymer ispolyacrylic acid.

In an exemplary embodiment, the viscous polymer comprises a linearpolymer such as a polyacrylamide, a guar, a guar derivative, glycerol, apolysaccharide such as cellulose and starch, or a combination thereof.Without wishing to be bound by theory, it is believed that the presenceof a viscous polymer in the hydraulic fracturing composition increasesthe viscosity, thus the proppant-suspension ability of the composition.The presence of the viscous polymer also helps to reduce the frictionpressure. When the hydraulic fracturing composition is a foam fluid, theviscous polymer further stabilizes the foam fluid by improving the foamquality and foam half-life.

The viscous polymer forms a viscous gel due to contact with the fluid ofthe hydraulic fracturing composition (or another fluid such as water,brine, or other downhole fluid). When the viscous polymer comprisesglycerol, a linear polymer such as linear polyacrylamide, a guar, a guarderivative, a polysaccharide such as cellulose and starch, or acombination thereof, the formed viscous gel can be referred to as alinear gel. In some embodiments, a combination of fluids is used, afirst fluid to expand the SAP and a second fluid to gel the viscosepolymer. Without wishing to be bound by theory, it is believed that theviscous polymer has increased viscosity due to long polymer chains thatbecomes entangled. Entangled polymer chains of the viscous polymercreates networks, giving complex viscosity behavior. In an embodiment,the viscous polymer is a copolymer that contains two or more differentmonomers that are arranged randomly or in blocks. Moreover, theviscosity of the viscous polymer is increased by crosslinking thepolymer chains of the viscose polymer. Crosslinkers for the viscouspolymer include borate, titanate, zirconate, aluminate, chromate, or acombination thereof. Boron crosslinked viscose polymers include, e.g.,guar and substituted guars crosslinked with boric acid, sodiumtetraborate, or encapsulated borates; borate crosslinkers may be usedwith buffering agents and pH control agents such as sodium hydroxide,magnesium oxide, sodium sesquicarbonate, and sodium carbonate, amines(such as hydroxyalkyl amines, anilines, pyridines, pyrimidines,quinolines, and pyrrolidines, and carboxylates such as acetates andoxalates) and with delay agents such as sorbitol, aldehydes, and sodiumgluconate. Zirconium crosslinked viscose polymers include, e.g., thosecrosslinked by zirconium lactates (e.g., sodium zirconium lactate),triethanolamines, 2,2′-iminodiethanol, or a combination thereof.Titanates for crosslinking include, e.g., lactates and triethanolamines,and the like.

In an embodiment, the hydraulic fracturing composition includes an SAP,for example an SAP having crosslinked polymer particles such as apolyacrylic acid, polyacrylamide, a polysaccharide, or a combinationthereof a plurality of proppant particles; a fluid to expand the SAP,and a viscose polymer. Once the SAP is combined with the fluid, itexpands while maintaining its shape. The viscous polymer is a linearpolymer that hydrates in the fluid and has a viscosity determined byentanglement of the hydrated linear polymer. It is contemplated that theentangled linear polymers can be crosslinked in-situ to form acrosslinked gel. Thus, the hydraulic fracturing composition hasbeneficial rheological properties including tunable viscosity andbreaking properties.

The hydraulic fracturing composition can also comprise a surfactant.Useful surfactants include fatty acids of up to 22 carbon atoms such asstearic acids and esters and polyesters thereof, poly(alkylene glycols)such as poly(ethylene oxide), poly(propylene oxide), and block andrandom poly(ethylene oxide-propylene oxide) copolymers such as thosemarketed under the trademark PLURONIC by BASF. Other surfactants includepolysiloxanes, such as homopolymers or copolymers ofpoly(dimethylsiloxane), including those having functionalized endgroups, and the like. Other useful surfactants include those having apolymeric dispersant having poly(alkylene glycol) side chains, fattyacids, or fluorinated groups such as perfluorinated C₁₋₄ sulfonic acidsgrafted to the polymer backbone. Polymer backbones include those basedon a polyester, a poly(meth)acrylate, a polystyrene, apoly(styrene-(meth)acrylate), a polycarbonate, a polyamide, a polyimide,a polyurethane, a polyvinyl alcohol, or a copolymer comprising at leastone of these polymeric backbones. Additionally, the surfactant isanionic, cationic, zwitterionic, or non-ionic.

Exemplary cationic surfactants include but are not limited to alkylprimary, secondary, and tertiary amines, alkanolamides, quaternaryammonium salts, alkylated imidazolium, and pyridinium salts. Additionalexamples of the cationic surfactant include primary to tertiaryalkylamine salts such as, e.g., monostearylammonium chloride,distearylammonium chloride, tristearylammonium chloride; quaternaryalkylammonium salts such as, e.g., monostearyltrimethylammoniumchloride, distearyldimethylammonium chloride,stearyldimethylbenzylammonium chloride,monostearyl-bis(polyethoxy)methylammonium chloride; alkylpyridiniumsalts such as, e.g., N-cetylpyridinium chloride, N-stearylpyridiniumchloride; N,N-dialkylmorpholinium salts; fatty acid amide salts such as,e.g., polyethylene polyamine; and the like.

Exemplary anionic surfactants include alkyl sulfates, alkyl sulfonates,fatty acids, sulfosuccinates, and phosphates. Examples of an anionicsurfactant include anionic surfactants having a carboxyl group such assodium salt of alkylcarboxylic acid, potassium salt of alkylcarboxylicacid, ammonium salt of alkylcarboxylic acid, sodium salt ofalkylbenzenecarboxylic acid, potassium salt of alkylbenzenecarboxylicacid, ammonium salt of alkylbenzenecarboxylic acid, sodium salt ofpolyoxyalkylene alkyl ether carboxylic acid, potassium salt ofpolyoxyalkylene alkyl ether carboxylic acid, ammonium salt ofpolyoxyalkylene alkyl ether carboxylic acid, sodium salt ofN-acylsarcosine acid, potassium salt of N-acylsarcosine acid, ammoniumsalt of N-acylsarcosine acid, sodium salt of N-acylglutamic acid,potassium salt of N-acylglutamic acid, ammonium salt of N-acylglutamicacid; anionic surfactants having a sulfonic acid group; anionicsurfactants having a phosphonic acid; and the like.

In an embodiment, the nonionic surfactant is, e.g., an ethoxylated fattyalcohols, alkyl phenol polyethoxylates, fatty acid esters, glycerolesters, glycol esters, polyethers, alkyl polyglycosides, amineoxides, ora combination thereof. Exemplary nonionic surfactants include fattyalcohols (e.g., cetyl alcohol, stearyl alcohol, cetostearyl alcohol,oleyl alcohol, and the like); polyoxyethylene glycol alkyl ethers (e.g.,octaethylene glycol monododecyl ether, pentaethylene glycol monododecylether, and the like); polyoxypropylene glycol alkyl ethers (e.g.,butapropylene glycol monononyl ethers); glucoside alkyl ethers (e.g.,decyl glucoside, lauryl glucoside, octyl glucoside); polyoxyethyleneglycol octylphenol ethers (e.g., Triton X-100 (octyl phenolethoxylate)); polyoxyethylene glycol alkylphenol ethers (e.g.,nonoxynol-9); glycerol alkyl esters (e.g., glyceryl laurate);polyoxyethylene glycol sorbitan alkyl esters (e.g., polysorbates such assorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate,sorbitan tristearate, sorbitan monooleate, and the like); sorbitan alkylesters (e.g., polyoxyethylene sorbitan monolaurate, polyoxyethylenesorbitan monopalmitate, polyoxyethylene sorbitan monostearate,polyoxyethylene sorbitan monooleate, and the like); cocamideethanolamines (e.g., cocamide monoethanolamine, cocamide diethanolamine,and the like); amine oxides (e.g., dodecyldimethylamine oxide,tetradecyldimethylamine oxide, hexadecyl dimethylamine oxide,octadecylamine oxide, and the like); block copolymers of polyethyleneglycol and polypropylene glycol (e.g., poloxamers available under thetrade name Pluronics, available from BASF); polyethoxylated amines(e.g., polyethoxylated tallow amine); polyoxyethylene alkyl ethers suchas polyoxyethylene stearyl ether; polyoxyethylene alkylene ethers suchas polyoxyethylene oleyl ether; polyoxyalkylene alkylphenyl ethers suchas polyoxyethylene nonylphenyl ether; polyoxyalkylene glycols such aspolyoxypropylene polyoxyethylene glycol; polyoxyethylene monoalkylatessuch as polyoxyethylene monostearate; bispolyoxyethylene alkylaminessuch as bispolyoxyethylene stearylamine; bispolyoxyethylene alkylamidessuch as bispolyoxyethylene stearylamide; alkylamine oxides such asN,N-dimethylalkylamine oxide; and the like.

Zwitterionic surfactants (which include a cationic and anionicfunctional group on the same molecule) include, e.g., betaines, such asalkyl ammonium carboxylates (e.g., [(CH₃)₃N⁺—CH(R)COO⁻] or sulfonates(sulfo-betaines) such as [RN⁺(CH₃)₂(CH₂)₃SO_(3−]), where R is an alkylgroup). Examples include n-dodecyl-N-benzyl-N-methylglycine[C₁₂H₂₅N⁺(CH₂C₆H₅)(CH₃)CH₂COO⁻], N-allyl N-benzyl N-methyltaurines[C_(n)H_(2n+1)N⁺(CH₂C₆H₅)(CH₃)CH₂CH₂SO₃ ⁻].

In an embodiment, the surfactant is a viscoelastic surfactant. Thesurfactant is viscoelastic because, unlike numerous surfactants, whichform Newtonian solutions with a viscosity slightly higher than watereven at high concentrations, it is capable of forming viscoelasticfluids at a lower concentration. This specific rheological behavior ismainly due to the types of surfactant aggregates that are present in thefluids. In low viscosity fluids, the surfactant molecules aggregate inspherical micelles whereas, in viscoelastic fluids, long micelles, whichcan be described as worm-like, thread-like or rod-like micelles, arepresent and entangle.

The viscoelastic surfactant of the invention is usually ionic. It may becationic, anionic or zwitterionic depending on the charge of its headgroup. When the surfactant is cationic, it is associated with a negativecounterion, which can be an inorganic anion such as a sulfate, anitrate, a perchlorate or a halide such as Cl, Br or with an aromaticorganic anion such as salicylate, naphthalene sulfonate, p and mchlorobenzoates, 3,5 and 3,4 and 2,4-dichlorobenzoates, t-butyl andethyl phenate, 2,6 and 2,5-dichlorophenates, 2,4,5-trichlorophenate,2,3,5,6-tetrachlorophenate, p-methyl phenate, m-chlorophenate,3,5,6-trichloropicolinate, 4-amino-3,5,6-trichlorpicolinate,2,4-dichlorophenoxyacetate. When the surfactant is anionic, it isassociated with a positive counterion, for example, Na+ or K+. When itis zwitternionic, it is associated with both negative and positivecounterions, for example, Cl and Na+ or K+. Other viscoelasticsurfactant has been described in U.S. Pat. Nos. 7,081,439 and 7,279,446.

The hydraulic fracturing composition can be a liquid or a foam. A liquidincludes a surfactant based fluid, a linear gel fluid, or a crosslinkedgel fluid. A surfactant-based fluid can refer to the hydraulicfracturing composition comprising a viscoelastic surfactant. A lineargel fluid can refer to the hydraulic fracturing composition comprising alinear gel. Similarly, a crosslinked gel fluid refers to the hydraulicfracturing composition comprising a crosslinked gel.

A foam fluid is a stable mixture of gas and liquid. It is generallydescribed by its foam quality, i.e. the ratio of gas volume to the foamvolume. The foam half-life is another important parameter to evaluatethe stability of foam fluids. The half-life of a foam fluid is the timenecessary for one-half of the liquid used to generate the foam to breakout of the foam under atmospheric conditions. A foam system is mainlyused in fracturing low pressure or water sensitive formations.

Water-soluble polymers, such as guar gums, high-molecular weightpolysaccharides composed of mannose and galactose sugars, or guarderivatives such as hydropropyl guar (HPG), carboxymethylhydropropylguar (CMHPG), can be used to prepare the liquid phase of the foamfluids. Crosslinking agents based on boron, titanium, zirconium oraluminum complexes can be used to increase the effective molecularweight of the polymer and make them better suited for use inhigh-temperature wells.

Polymer-free, liquid phase of foam fluids can be obtained usingviscoelastic surfactants. These fluids are normally prepared by mixingin appropriate amounts suitable surfactants such as anionic, cationic,nonionic and zwitterionic surfactants in aqueous solutions. Theviscosity of viscoelastic surfactant fluids is attributed to the threedimensional structure formed by the components in the fluids. When theconcentration of surfactants in a viscoelastic fluid significantlyexceeds a critical concentration, and in most cases in the presence ofan electrolyte, surfactant molecules aggregate into species such asmicelles, which can interact to form a network exhibiting viscosity andelastic behavior to further stabilize the foamed systems. Meanwhile, thesurfactant also acts as foaming agent to create the stable dispersion ofgas in viscous liquid.

In an embodiment, various additional additives are included in thehydraulic fracturing composition. Exemplary additional additives includea lubricant, a non-emulsifier, a clay stabilizer, a biocide, an acid, acorrosion inhibitor, a pH-adjusting agent, or a combination thereof.

In an embodiment, the non-emulsifier of the additional additive is acombination of the above surfactants or a combination of surfactant witha short chain alcohol or polyol such as lauryl sulfate with isopropanolor ethylene glycol. The non-emulsifier prevents formation of emulsionsin the hydraulic fracturing composition.

In an embodiment, the additional additive is the lubricant such as apolyacrylamide, petroleum distillate, hydrotreated light petroleumdistillate, a short chain alcohol (e.g., methanol), or polyol (e.g.,ethylene glycol or glycerol). Such lubricants minimize friction andinclude, e.g., a polymer such as polyacrylamide, polyisobutylmethacrylate, polymethyl methacrylate, or polyisobutylene as well aswater-soluble lubricants such as guar, guar derivatives, polyacrylamide,and polyethylene oxide. In an embodiment, the lubricant comprises aguar, a guar derivative, glycerol, polyacrylamide, a polysaccharide suchas cellulose and starch, or a combination thereof.

The clay stabilizer of the additional additive prevents the claydownhole from swelling under contact with the hydraulic fracturingcomposition or applied fracturing pressure. In an embodiment, the claystabilizer includes a quaternary amine, a brine (e.g., KCl brine),choline chloride, tetramethyl ammonium chloride, and the like.

According to an embodiment, the additional additive is the pH-adjustingagent, which adjusts pH of the hydraulic fracturing composition. ThepH-adjusting agent is an organic or inorganic base, organic or inorganicacid, or a buffering agent, which is any appropriate combination of acidand conjugate base. Exemplary inorganic bases include those representedby MOH, where M is a metal from group 1 or 2 of the periodic table, atransition metal, or a metal or metalloid from group 13, 14, or 15;carbonate salt; bicarbonate salt; or a combination thereof. Exemplaryinorganic acids include HCl, HBr, fluoroboric acid, sulfuric acid,nitric acid, acetic acid, formic acid, methanesulfonic acid, propionicacid, chloroacetic or dichloroacetic acid, citric acid, glycolic acid,lactic acid, or a combination thereof. In an embodiment, thepH-adjusting agent is selected to avoid imparting favorablecharacteristics to the hydraulic fracturing composition. In anembodiment, the pH-adjusting agent is selected to avoid damage to thesurface equipment containing the hydraulic fracturing composition or toavoid damaging the wellbore or subterranean formation.

In an embodiment, the additional additive to the hydraulic fracturingcomposition is the biocide that prevents injection of a microbe (e.g.,bacteria) downhole. The biocide kills, eliminates, or reduces bacteriain the hydraulic fracturing composition such as water (e.g., when usingriver water as the fluid). In this way, introduction of live bacteriainto the formation is prevented, thus reducing production of, e.g., sourgas.

According to an embodiment, the biocide does not interfere with theother components of the hydraulic fracturing composition and is not ahealth risk. In an embodiment, the biocide is an aldehyde such asglutaraldehyde. Examples of the biocide include non-oxidizing andoxidizing biocides. Exemplary oxidizing biocides include hypochloritebleach (e.g., calcium hypochlorite and lithium hypochlorite), peraceticacid, potassium monopersulfate, potassium peroxymonosulfate,bromochlorodimethylhydantoin, dichloroethylmethylhydantoin,chloroisocyanurate, trichloroisocyanuric acids, dichloroisocyanuricacids, chlorinated hydantoins, and the like. Additional oxidizingbiocides include, e.g., bromine products such as stabilized sodiumhypobromite, activated sodium bromide, or brominated hydantoins. Otheroxidizing biocides include chlorine dioxide, ozone, inorganicpersulfates such as ammonium persulfate, or peroxides, such as hydrogenperoxide and organic peroxides.

Exemplary non-oxidizing biocides include dibromonitfilopropionamide,thiocyanomethylthiobenzothlazole, methyldithiocarbamate,tetrahydrodimethylthladiazonethione, tributyltin oxide,bromonitropropanediol, bromonitrostyrene, methylene bisthiocyanate,chloromethylisothlazolone, methylisothiazolone, benzisothlazolone,dodecylguanidine hydrochloride, polyhexamethylene biguanide,tetrakis(hydroxymethyl)phosphonium sulfate, glutaraldehyde,alkyldimethylbenzyl ammonium chloride, didecyldimethylammonium chloride,poly[oxyethylene-(dimethyliminio)ethylene (dimethyliminio)ethylenedichloride], decylthioethanamine, terbutylazine, and the like.Additional non-oxidizing biocides are quaternary ammonium salts,aldehydes and quaternary phosphonium salts. In an embodiment, quaternarybiocides have a fatty alkyl group and three methyl groups, but in thephosphonium salts, the methyl groups, e.g., are substituted byhydroxymethyl groups without substantially affecting the biocidalactivity. In an embodiment, they also are substituted with an arylgroup. Examples include formaldehyde, glyoxal, furfural, acrolein,methacrolein, propionaldehyde, acetaldehyde, crotonaldehyde, pyridiniumbiocides, benzalkonium chloride, ceramide, cetyl trimethyl ammoniumchloride, benzethonium chloride, cetylpyridinium chloride,chlorphenoctium amsonate, dequalinium acetate, dequalinium chloride,domiphen bromide, laurolinium acetate, methylbenzethonium chloride,myristyl-gamma-picolinium chloride, ortaphonium chloride, triclobisoniumchloride, alkyl dimethyl benzyl ammonium chloride, cocodiamine, dazomet,1-(3-chloroallyl)-chloride.3,5,7-triaza-1-azoniaadamantane, or acombination thereof.

In an embodiment, the biocide is encapsulated or coated as discussedabove with regard to the proppant particles or breaker. In anembodiment, the biocide is encapsulated or coated by any suitableencapsulation method using any suitable encapsulation material. Theencapsulation material is any material that does not adversely interactor chemically react with the biocide to destroy its utility. In anembodiment, the biocide is released from the coating at a selected time.

In the hydraulic fracturing composition, the proppant particles arepresent in an amount effective to prop open the fracture without thegeometry of the fracture being altered during settling of the formationwhen the proppant is released from the SAP. In a particular embodiment,the proppant particles are present in a mass concentration from 0.1pounds per gallon (lb/gal) to 20 lb/gal, specifically 0.25 lb/gal to 16lb/gal, and more specifically 0.25 lb/gal to 12 lb/gal, based on thetotal volume of the composition. In an embodiment, the SAP is present ina mass concentration from 1 pound of SAP per one thousand gallons offluid (ppt) to 200 ppt, specifically 5 ppt to 100 ppt, and morespecifically 15 ppt to 50 ppt, based on the total volume of thecomposition. In the hydraulic fracturing composition, any ratio of theamount of the proppant particles to the amount of the SAP is applicableas long as the proppant particles are suspended in the gel formed by theSAP.

In an embodiment, the breaker is present in the hydraulic fracturingcomposition in a mass concentration from 0 ppt to 20 ppt, specifically 0ppt to 15 ppt, and more specifically, 0 ppt to 10 ppt, based on thetotal volume of the composition. In some embodiments, the biocide ispresent in an amount from 10 parts per million (ppm) to 2000 ppm,specifically 50 ppm to 1500 ppm, and more specifically 50 ppm to 1000ppm. An amount of the viscose polymer, if present, is from 0.25 gallonsof viscose polymer per 1000 gallons of fluid (gpt) to 10 gpt,specifically 0.5 gpt to 8 gpt, and more specifically 0.5 gpt to 4 gpt,based on the total hydraulic fracturing composition volume.

The hydraulic fracturing composition can be made in a variety of ways.According to an embodiment, a process for making the hydraulicfracturing composition includes contacting a superabsorbent polymer witha fluid to expand the superabsorbent polymer into an expanded state anddisposing a plurality of proppant particles in the superabsorbentpolymer to make the hydraulic fracturing composition. As shown in FIG.3, the SAP (e.g., particle 12 or fiber 50) is in an unexpanded state 20with internal crosslinks 14 and has a diameter of D2 prior to contactwith the fluid (not shown). As indicated in FIGS. 1 and 2, oncecontacted with the fluid, the SAP (12 or 50) expands to diameter D1(where D1 is greater than D2) as the fluid is absorbed into the SAP (12or 50). Additionally, in the case of an SAP fiber 50 or an SAP that hasa major axis, the length of the SAP 50 can lengthen upon expansioncaused by absorption of the fluid. It should be noted that thecrosslinks 14 limit the volumetric expansion and the ultimate size ofthe SAP 12. In the expanded state (FIG. 1 or FIG. 2), the proppantparticles 18 are disposed in the SAP (12 or 50). The SAPs (12 or 50)shown in FIG. 1, FIG. 2, and FIG. 3 represent a single particle, fiber,etc. of the SAP 12 or a plurality of such items as well as agglomeratesof polymer chains that make the SAP (12 or 50).

The additive including the scale inhibitor, tracer, buffering agent, ora combination thereof, can be added to the fluid before or afterdisposing the SAP (12 or 50) and the proppant particles 18. Optionally,the additive is added to the SAP and proppant particles. According to anembodiment, the breaker is added to the fluid before or after disposingthe SAP (12 or 50) and the proppant particles 18. Optionally, thebreaker is added to the SAP and proppant particles.

In an embodiment, combining the components of the hydraulic fracturingcomposition is accomplished in a vessel such as a mixer, blender, andthe like. In some embodiments, the hydraulic fracturing composition isinjected without mixing, e.g. it is injected “on the fly”. Thecomponents are mixed, agitated, stirred, and the like. In an embodiment,the components are combined as the hydraulic fracturing composition isbeing disposed downhole.

The hydraulic fracturing composition herein has advantageous propertiesthat include suspending the proppant particles in the SAP for anextended period of time or at an elevated temperature or pressure. Thelength of time, temperature, or pressure under which the proppantparticles remain suspended in the SAP is determined by the polymerchains that make up the SAP as well as the crosslinker compound, degreeof crosslinking, amount of proppant particles present, concentration ofthe SAP, and identity of the fluid.

Accordingly, the hydraulic fracturing composition includes a highlycrosslinked SAP, lightly crosslinked SAP, or a combination thereof. Inthe hydraulic fracturing composition, the SAP is configured to be brokenand to release the proppant particles in response to the breakingcondition. The breaking condition includes a temperature, pH, contactbetween the breaker and the SAP, a time lapse between the SAP being inthe expanded state and breaking the superabsorbent polymer. In anembodiment, the time the proppant particles are disposed in the SAPprior to release from the SAP is greater than or equal to 48 hours at atemperature greater than or equal to 150° F., specifically greater thanor equal to 36 hours, more specifically greater than or equal to 24hours, even more specifically greater than or equal to 18 hours, and yetmore specifically greater than or equal to 20 minutes, preferably from10 minutes to 18 hours.

In an embodiment, the pH for breaking the SAP is a pH effective to breakbonds in the SAP, crosslinker, between the SAP and crosslinker, or acombination thereof. Likewise, in an embodiment, the pH causesdissociation between particles of SAP so that the proppant particles arereleased therefrom. In an embodiment, the pH is acidic or basic so thationic groups of the polymer chains in the SAP are neutralized, whichaffects the amount of fluid present in the SAP and causes contraction ofthe SAP and expulsion of the proppant particles. According to anembodiment, the pH is from 1 to 12, specifically 3 to 12, and morespecifically 5 to 11.5.

In an embodiment, the SAP breaks due to the breaking condition even inthe absence of the breaker. Thus, in an embodiment, the SAP is broken ata temperature, pH, time lapse, and the like without contact with thebreaker.

In an embodiment, the viscosity of the SAP in the expanded state is from1 centipoise (cP) to 1000 cP, and specifically 1 cP to 300 cP, asmeasured by Ofite M900 rheometer for less than 100 cP viscosity or GraceM5500 rheometer for more than 100 cP viscosity at a temperature of 180°F.

The hydraulic fracturing composition is useful e.g., to transport anddispose proppant particles in a fracture without the SAP being brokenuntil after disposal of the proppant particles to prevent proppantparticles from settling and therefore increase overall fractured surfacearea. According to an embodiment, the hydraulic fracturing compositionis used to form the fracture. In an embodiment, a process for disposinga plurality of proppant particles in a fracture includes disposing ahydraulic fracturing composition in a downhole environment. Thehydraulic fracturing composition includes an SAP in an expanded stateand configured to break in response to a breaking condition, such that adecomposed polymer is formed from the superabsorbent polymer. Thehydraulic fracturing composition also includes a plurality of proppantparticles disposed in the SAP prior to release of the plurality ofproppant particles from the SAP in response to breaking the SAP, anadditive comprising a scale inhibitor, tracer, buffer, or combinationthereof, and a fluid to expand the SAP into the expanded state. In thismethod, forming a fracture in the downhole environment is accomplishedby applying hydraulic force on the downhole environment from thehydraulic fracturing composition, disposing the hydraulic fracturingcomposition in the fracture, breaking the superabsorbent polymer afterforming the fracture, and releasing the plurality of proppant particlesfrom superabsorbent polymer to dispose the plurality of proppantparticles in the fracture. In this manner, the proppant particles do notsettle to the bottom of the fracture. The downhole environment is, e.g.,a reservoir temperature, formation water, formation rock, sand, and thelike, which contains, e.g., pores or veins of various sizes in suchrock, sand, and the like.

As shown in FIG. 4, after the breaking condition occurs, the SAP is in abroken state 30 such that the SAP forms, e.g., a decomposed polymer 32with the proppant particles 18 released from the SAP. Although thedecomposed polymer 32 is shown as being separated fragments (e.g.,polymers, oligomers, monomers, molecules, atoms, and the like, which arecharged or charge neutral), in an embodiment, the decomposed polymer isformed from the SAP by breaking all or some of the crosslinks so thatthe polymer chains of the SAP remain intact. It is contemplated thatconformational changes in the SAP release the proppant particles fromthe SAP and ensure good conductivity.

In an embodiment, the crosslinks or the SAP are degraded by certainconditions such as heat or pH. Degradation reduces the degree ofcrosslinking in the SAP by breaking a bond in the crosslinker or a bondbetween the crosslinker and polymer chains of the SAP. Generally,decreasing the degree of crosslinking of the SAP increases the amount offluid that is absorbed by the SAP or increases the volumetric increaseof the SAP due to fluid absorption. In an embodiment, the aforementionedconditions cleave bonds in the crosslinks without substantiallydegrading the polymer backbone of the SAP. In some embodiments, theseconditions also degrade the polymer backbone of the SAP.

In addition to disposing the hydraulic fracturing composition in thedownhole environment for hydraulically fracturing the formation, themethod also includes disposal of other elements such as water, adownhole fluid (e.g., brine or other above-mentioned fluids), a viscosepolymer, or a combination thereof. Thus, in an embodiment, the methodfurther includes disposing water, a viscose polymer, or a combinationthereof in the downhole environment and forming the fracture with thehydraulic fracturing composition, water, the viscose polymer, or acombination thereof. The order of addition can be varied and the time ofinjecting each is the same or different. According to an embodiment, forhydraulically fracturing a formation, a proppant-free fluid and aproppant-containing fluid are injected in an alternating order into asubterranean formation. The proppant-free fluid can be injected firstfollowed by the proppant-containing fluid. Alternatively, theproppant-containing fluid is injected first followed by theproppant-free fluid.

In an exemplary embodiment, the proppant-free fluid comprises an aqueouscarrier comprising water, brine, an acid, or a base and a lubricant. Thelubricant can comprise a polyacrylamide, a guar, a guar derivative,glycerol, a polysaccharide such as cellulose and starch, or acombination thereof. When the lubricant comprises a polyacrylamide, e.g.MaxPerm 20A, MaxPerm 20A is present in an amount of 0.25 to 15 gallonsper one thousand gallons of the proppant-free fluid. When the lubricantcomprises a guar, the lubricant is present in an amount of 1 to 50pounds per one thousand gallons of the proppant-free fluid. Theproppant-containing fluid comprises SPP, a plurality of proppantparticles disposed in SPP, a fluid to expand the SPP into the expandedstate, and optionally a linear gel or a viscous polymer comprising aguar, a guar derivative, a polyacrylamide, glycerol, a polysaccharide,or a combination thereof. The proppant-containing fluid can be thehydraulic fracturing composition disclosed herein. By using the method,high conductivity channels are created within the proppant pack. Theeffects are illustrated in FIG. 15.

In another exemplified embodiment, the proppant-free fluid comprisesSPP, a fluid to expand the SPP, and optionally a viscous polymercomprising a guar, a guar derivative, a polyacrylamide, glycerol, apolysaccharide, or a combination thereof. For proppant free fluid, 20-60pounds SPPs are normally prepared in one thousand gallons ofproppant-free fluids. Proppant containing fluids comprises an aqueouscarrier comprising water, brine, an acid, or a base, proppants, and alubricant. The lubricant can comprise a polyacrylamide, a guar, a guarderivative, glycerol, a polysaccharide, or a combination thereof. Whenthe lubricant comprises a polyacrylamide, e.g. MaxPerm 20A, MaxPerm 20Ais present in an amount of 0.25 to 15 gallons per one thousand gallonsof the proppant-free fluid. When the lubricant comprises a guar, thepolymer is present in an amount of 1 to 50 pounds per one thousandgallons of the proppant-containing fluid. Heterogeneous proppantdistribution can be achieved by this method. The beneficial effects areillustrated in FIG. 16.

In an embodiment, the initial injection of water (or brine) and theviscous polymer is, e.g., 15 minutes each although the length ofinjection times is different in some embodiments. The injection time forthe hydraulic fracturing composition is the same or different as thewater or viscose polymer, e.g., having a duration of two hours. It iscontemplated that the injection time varies and is selected based onconditions of the formation and the properties of the hydraulicfracturing composition, other fluids (e.g., brine), viscose polymer, andthe like.

A benefit of the hydraulic fracturing composition is that the proppantparticles remain disposed in the SAP until the breaking condition causesthe SAP to break. As shown in FIG. 5, a formation 100 is traversed by atubular 104 disposed in casing 102 although only the casing 102 or onlythe tubular 104 is present in some embodiments. The hydraulic fracturingcomposition 120 is transferred from an interior of the tubular 104 tocontact the formation 100 through an aperture (not shown) in the tubular104. The hydraulic fracturing composition 120 (which is similar to oridentical to that of FIG. 1 or FIG. 2) fractures the formation 100 tocreate a fracture 106. The proppant particles 18 are disposed in the SAP12 until the breaking condition occurs at which point the SAP 12 breaksto form a decomposed polymer 122 and releases the proppant particles 18as shown in FIG. 6. Here, the SAP 12 is not broken nor are the proppantparticles 18 released from the SAP 12 before closing of the fracture106. Therefore, the proppant particles 18 do not settle to the bottom ofthe fracture 106 before the fracture 106 closes so that the geometry ofthe fracture 106 is not affected negatively by breaking the SAP 12. Thatis, before the fracture 106 closes, it has a height H1. After closing,the fracture has a height H2. After closing of the fracture commences,the SAP 12 is broken, and the decomposed polymer 122 is formed. Due tothe high degree of suspension of the proppant particles 18 in the SAP12, the height H2 of the fracture 106 does not vary significantly fromthe original, pre-closing height H1, such that the height H2(post-closing) is nearly the same size as the original height H1(pre-closing).

During the breaking of SAP 12, the formation pressure squeezes theproppant particles in-situ from settling to the bottom of the fractureby the broken fluids leaking off. In this manner, the hydraulicfracturing composition accomplishes enhanced proppant particlestransport and vertical distribution in the fracture. Consequently, theconduction of hydrocarbons or other fluids from the formation 100,through the fracture 106, into the tubular 104 (or a space between thetubular 104 and casing 102) is increased relative to incomplete orimperfect disposal of the proppant particles 18, which is shown in FIGS.7 and 8. Therefore, the hydraulic fracturing composition 120 transportsand disposes the proppant particles 18 to ensure that the proppantparticles 18 prop open the fracture 106 in the same or substantially thesame geometry as the fracture 106 is initially formed and thus providesmore fractured surface area than if the proppant particles settle to thebottom of the fracture as shown in the FIGS. 7 and 8. In this manner, ahigh conduction pathway for transmission of hydrocarbons and otherfluids between the formation and the borehole occurs when using thehydraulic fracturing composition herein.

With regard to FIG. 7 and FIG. 8, when using certain fracturing systemsthat do not contain the hydraulic fracturing composition herein, such asproppant particles 130 suspended in a fluid 132 without the benefit ofthe SAP to suspend the proppant particles 130, the proppant particles130 settle from the fluid 132 and collect on the bottom of the fracture106 before the fracture 106 closes (FIG. 7). Even though the fracture106 has an original height H2 before closing (FIG. 7), the height H2 isreduced to a diminished height H4 after closing because the proppantparticles 130 settle to the bottom of the fracture 106 before thefracture 106 closed.

The hydraulic fracturing composition and processes herein areillustrated further by the following non-limiting example.

Superabsorbent polymer (SAP) (QX-A1051; Nippon Shokubai) was mixed withtap water at a concentration of 40 parts per thousand (ppt) (w/v). ThepH of the mixture was determined to be about 7. The pH was adjusted togreater than 7 using the buffer BF-10L (from Baker Hughes) and a pH ofless than 7 using the buffer BF-9L from Baker Hughes. The viscosity ofthe mixtures at different pH's was recorded using a Chandler M5550instrument according to the API RP 39 standard at 20° C. and underatmospheric pressure. FIG. 17 is a plot showing the effect of pH onviscosity for this example. As shown in FIG. 17, a maximum viscosity wasrecorded at a fluid pH about 7 to about 8.

All ranges disclosed herein are inclusive of the endpoints, and theendpoints are independently combinable with each other. The ranges arecontinuous and thus contain every value and subset thereof in the range.Unless otherwise stated or contextually inapplicable, all percentages,when expressing a quantity, are weight percentages. As used herein,“combination” is inclusive of blends, mixtures, alloys, reactionproducts, and the like. Further As used herein, “a combination thereof”refers to a combination comprising at least one of the namedconstituents, components, compounds, or elements, optionally togetherwith one or more like constituents, components, compounds, or elementsnot named. The use of the terms “a” and “an” and “the” and similarreferents in the context of describing the invention (especially in thecontext of the following claims) are to be construed to cover both thesingular and the plural, unless otherwise indicated herein or clearlycontradicted by context. “Or” means “and/or.” The conjunction “or” isused to link objects of a list or alternatives and is not disjunctive;rather the elements can be used separately or can be combined togetherunder appropriate circumstances.

It should further be noted that the terms “first,” “second,” “primary,”“secondary,” and the like herein do not denote any order, quantity, orimportance, but rather are used to distinguish one element from another.The modifier “about” used in connection with a quantity is inclusive ofthe stated value and has the meaning dictated by the context (e.g., itincludes the degree of error associated with measurement of theparticular quantity). All references are incorporated herein byreference.

While one or more embodiments have been shown and described,modifications and substitutions may be made thereto without departingfrom the spirit and scope of the invention. Accordingly, it is to beunderstood that the present invention has been described by way ofillustrations and not limitation. Embodiments herein can be usedindependently or can be combined.

1. A hydraulic fracturing composition comprising: a superabsorbentpolymer in an expanded state and configured to break in response to abreaking condition; a plurality of proppant particles disposed in thesuperabsorbent polymer prior to release of the plurality of proppantparticles from the superabsorbent polymer in response to breaking thesuperabsorbent polymer; a well treatment agent comprising a scaleinhibitor, a tracer, a pH buffering agent, or a combination thereof, anda fluid to expand the superabsorbent polymer into the expanded state. 2.The hydraulic fracturing composition of claim 1, wherein thesuperabsorbent polymer comprises a repeat unit derived from an acrylate,an acrylamide, a vinylpyrrolidone, a vinyl acetate, a vinyl alcohol, asaccharide, a 2-acrylamide-2-methylpropanesulfonic acid, a derivativethereof, or a combination thereof; and wherein the superabsorbentpolymer comprises a plurality of crosslinks.
 3. The hydraulic fracturingcomposition of claim 1, comprising about 0.001 to about 5 wt % of thescale inhibitor, based on the total weight of the hydraulic fracturingcomposition.
 4. The hydraulic fracturing composition of claim 3, whereinthe scale inhibitor comprises a carboxylic, sulfonic, or phosphonicacid-containing compound, a carboxylic, sulfonic, orphosphonic-containing polymer, or a combination thereof.
 5. Thehydraulic fracturing composition of claim 3, wherein the scale inhibitorcomprises an amino trimethylene phosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, 2-phosphonobutane-1,2,4-tricarboxylicacid, 2-hydroxyethyl-amino-bis(methylenephosphonic acid),ethylenediamine tetrakis(methylene phosphonic acid),tetramethylenediamine tetrakis(methylene phosphonic acid),hexamethylenediamine tetrakis(methylene phosphonic acid), 2-hydroxyphosphonoacetic acid, diethylene triamine penta(methylene phosphonicacid), bis(hexamethylenetriamine penta(methylene phosphonic acid),polyaminopolyether methylenephosphonate or a salt thereof,phosphino-polycarboxylate, polyacrylic acid, polymaleic acid, acryliccopolymer, sulfonate polyacrylate co-polymer, polyvinyl sulfonate,carboxymethyl inulin, polyaspartate, or a combination thereof.
 6. Thehydraulic fracturing composition of claim 1, comprising about 0.001 to10 wt % of the tracer, based on the total weight of the hydraulicfracturing composition.
 7. The hydraulic fracturing composition of claim6, wherein the tracer comprises a fluorinated benzoic acid,perfluorinated hydrocarbon, alcohol, ketone, organic acid, halogenatedcompound, or a combination thereof.
 8. The hydraulic fracturingcomposition of claim 7, wherein the tracer is encapsulated, coated,incorporated into a binder, adsorbed onto a matrix, or absorbed into amatrix.
 9. The hydraulic fracturing composition of claim 1, comprisingabout 0.01 to about 10 wt % of the pH buffering agent, based on thetotal weight of the hydraulic fracturing composition.
 10. The hydraulicfracturing composition of claim 9, wherein the pH buffering agentmaintains the pH of the hydraulic fracturing composition at about 6 toabout
 9. 11. The hydraulic fracturing composition of claim 9, whereinthe pH buffering agent maintains the pH of the hydraulic fracturingcomposition at about 7 to about
 8. 12. The hydraulic fracturingcomposition of claim 9, wherein the pH buffering agent is alkali oralkaline earth salt of a carbonate, a citrate, a gluconate, a phosphateor a tartrate, an oxide of an alkaline earth metal, an organicpolyelectrolyte, or a combination thereof.
 13. The hydraulic fracturingcomposition of claim 1, wherein the hydraulic fracturing compositioncomprises the pH buffering agent and further comprises a slow-releaseacid.
 14. The hydraulic fracturing composition of claim 13, wherein theslow-release acid comprises glyoxal, an encapsulated acid, a coatedacid, or a combination thereof.
 15. The hydraulic fracturing compositionof claim 1, further comprising a breaker, wherein the breaker comprisesa peroxide, a persulfate, a peracid, or a combination thereof.
 16. Thehydraulic fracturing composition of claim 15, wherein the breaker isencapsulated in an encapsulating material to prevent the breaker fromcontacting the superabsorbent polymer, and the encapsulating material isconfigured to release the breaker.
 17. The hydraulic fracturingcomposition of claim 16, wherein the superabsorbent polymer is presentin a mass concentration from 1 ppt to 200 ppt, based on total volume ofthe composition, the plurality of proppant particles is present in amass concentration from 0.1 lb/gal to 12 lb/gal, based on the totalvolume of the composition, and the breaker is present in a massconcentration from 0 ppt to 20 ppt, based on the total volume of thecomposition.
 18. A process for disposing a plurality of proppantparticles in a fracture, the process comprising: disposing a hydraulicfracturing composition in a fracture in a downhole environment, thehydraulic fracturing composition comprising: a superabsorbent polymer inan expanded state and configured to break in response to a breakingcondition, such that a decomposed polymer is formed from thesuperabsorbent polymer, a plurality of proppant particles disposed inthe superabsorbent polymer prior to release of the plurality of proppantparticles from the superabsorbent polymer in response to breaking thesuperabsorbent polymer, a well treatment agent comprising a scaleinhibitor, a tracer, a pH buffering agent, or a combination thereof, anda fluid to expand the superabsorbent polymer into the expanded state;and breaking the superabsorbent polymer after disposing in the fracture;and releasing the plurality of proppant particles from thesuperabsorbent polymer to dispose the plurality of proppant particles inthe fracture.
 19. The process of claim 19, further comprising decreasingundesired effects caused by scale formation, salt formation, paraffindeposition, asphaltene deposition, foaming agent deposition,emulsification, gas hydrate formation, corrosion, foaming agents, oxygenscavengers, H₂S scavengers, biocides, surfactants, or a combinationthereof, compared to a composition without the well treatment agent. 20.The process of claim 19, wherein the hydraulic fracturing compositioncomprises the pH buffering agent and a slow-release acid, and theprocess further comprises lowering the pH of the hydraulic fracturingcomposition past the buffering range of the buffering agent before thebreaking of the superabsorbent polymer.